This invention relates to composites containing thermoplastic resins, and particularly to thermoset composites containing a thermoplastic resin additive. The invention is especially directed to encapsulating or coating thermoplastic resin particles to control the physical properties of the thermoplastic or to act as a binder for such particles, and to encapsulating thermoplastic additives for incorporation into thermosets.
U.S. Pat. No. 4,954,195 discloses a process for producing thermoset composites having improved damage tolerance by mixing particles of a thermoplastic such as a polyimide having a specified particle size range, with a hot thermosetting resin such as a bismaleimide, employing up to about 40% of the thermoplastic by weight of the mixture, the particles of thermoplastic being insoluble in the resin mixture. The hot resin dispersion is then applied to fiber reinforcement such as carbon fibers to form pre-pregs, and upon curing the thermoset at elevated temperature the thermoplastic particles dissolve in the thermosetting resin, forming a composite with no definable boundary interfaces between the thermoplastic and thermosetting resins.
While the above process has proved generally successful for the production of improved damage tolerant composites, when relatively large amounts of the thermoplastic particles are used in the mixture with the thermosetting resin, the flow of the liquid thermosetting resin becomes inhibited and also there is a tendency for some of the thermoplastic particles to dissolve undesirably in the thermosetting resin prior to curing thereof. Thus, under these conditions, both the effectiveness of the thermoplastic additive in the thermosetting resin and the processibility of the mixture is reduced.
When fabricating thermoplastic powder impregnated pre-pregs, a solvent slurry of the thermoplastic powder, e.g. a polyimide, is applied to the reinforcement fibers and the solvent is evaporated, permitting the powder to adhere to the reinforcement fibers. In this procedure a solvent is added to the thermoplastic powder as a tackifier to adhere the thermoplastic particles to the fibers in producing the pre-preg. Employing such procedure it is difficult to obtain a consistent product and removal of the solvent is necessary.
The application of gel coats is known in the latex and pharmaceutical industries, e.g. for application to medicinal capsules, as for time release of the medicinal component. However, such concept has heretofore not been applied to resins for the production of thermoplastic and thermosetting resin composites.
An object of the present invention is the provision of improved procedure for the production of thermoplastic and thermosetting composites.
Another object is to provide procedure for controlling the physical properties of the thermoplastic when used as an additive in combination with the thermosetting resin for producing thermoset composites, as in the process of above U.S. Pat. No. 4,954,195.
Still another object is to provide improved procedure for producing thermoplastic impregnated pre-pregs without the use of solvents for the thermoplastic, which require removal after application.
A still further object is the application of gel coatings in the above procedures for producing thermoplastic and thermosetting pre-pregs and composites.
Yet another object is the provision of improved thermoplastic and thermoplastic-thermosetting pre-pregs and composites employing the above procedures.
Other objects and advantages of the invention will be apparent from the description below of the invention.